The present invention relates to an apparatus and a method for injecting a very small quantity of fluids necessary in such fields as information/precision equipment, machine tools, FA (Factory Automation) or in various manufacturing steps for semiconductors, liquid-crystals, displays, and surface mounting, and is particularly suitable for fluid injection apparatus and method for injecting fluids continuously or intermittently.
Fluid dispensing apparatuses (dispensers), which have conventionally been used in various fields, are now required to have a technology for feeding and controlling a very small quantity of fluid materials at high accuracy and with stability in response to the needs of electronic components smaller in size, and higher in recording density in recent years. For example, in the field of displays such as plasma displays, CRTs (Cathode Ray Tubes), organic ELs (Electro-Luminescences), there is a large demand for direct patterning of phosphors or electrode materials on panel faces without any mask, instead of conventional techniques such as screen printing and photo lithography. The dispensers have difficulties to be overcome for satisfying the demand as outlined below:
(i) miniaturization of a dispensing quantity
(ii) achievement of high accuracy in dispensing quantity
(iii) reduction in dispensing time
Conventionally, shown in FIG. 36 is a dispenser of air pulse method which has been widely used as a liquid dispensing apparatus, and the technology thereof has been introduced for example in “Automation Technology '93, Vol. 25 No. 7”.
The dispenser of this method is structured such that a constant flow of air fed from a constant pressure source is applied as a pulse to an inside 601 of a container 600 (cylinder) and liquid of a specific quantity corresponding to an increased portion of pressure in the cylinder 600 is discharged from a nozzle 602.
In the field of circuit formation which are achieving higher accuracy and more ultra miniaturization in recent years or in the field of manufacturing steps for electrodes and ribs of image tubes such as PDPs and CRTs, phosphor screen formation, liquid-crystals, and optical discs, most of fluids which need to be discharged in very small quantity are high-viscosity powder and granular materials.
The largest difficulty is how to discharge powder and granular materials including fine particles onto target substrates at high speed and high accuracy and with high reliability without causing clogging of flow passages.
For the purpose of high-speed intermittent discharge, a dispenser (hereinbelow referred to as a jet-type for the sake of convenience) as shown in FIG. 37 has been put into practical use. Reference numeral 550 denotes a micrometer, 551 a spring, 552 a piston seal member, 553 a piston chamber, 554 a heater, 555 a needle, 556 a discharge material flowing toward a seat portion, and 557 a dot-like discharge material flying from the dispenser. FIG. 38A and FIG. 38B are model views showing a discharge portion area 558 in FIG. 37, in which FIG. 38A shows a suction step while FIG. 38B shows a discharge step. Reference numeral 559 denotes a spherically-shaped convex portion formed on the discharge-side end portion of the needle 555, 560 a discharge tip portion, 561 a spherically-shaped concave portion formed on the discharge tip portion, and 562 a discharge nozzle. Reference numeral 563 denotes a pump chamber formed by the spherically-shaped convex portion 559 and concave portion 561.
In FIG. 38A showing the suction step, when a supply air pulse of the piston chamber 553 is ON, the needle 555 goes up against the spring 551. At this time, the suction portion 564 formed in between the spherically-shaped convex portion 559 and concave portion 561 is put in an open state, so that the discharge material 556 is filled in the pump chamber 563 from the suction portion 564. In FIG. 38B showing the discharge step, when the air pulse is OFF, that is, when an air pressure is not applied to the piston chamber 553, the needle 555 goes down by the force of the spring 551. At this time, the suction portion 564 is put in a closed state and so the fluid in the pump chamber 563 is compressed in an enclosed space except the discharge nozzle 562, by which high pressure is generated and the fluid flies and flows away.
Hereinbelow, a step for forming phosphor layers for plasma display panels will be taken as an example to state the issues of the prior art.
[1] Issue in screen printing method and photo lithography method
[2] Issue in the case where the phosphor layers are subjected to direct patterning with use of the conventional dispenser technology
First, description will be given of the issue [1].
(1) Structure of Plasma Display Panels
FIG. 39 shows one example of the structure of a plasma display panel (hereinbelow referred to as PDP). The PDP is mainly composed of a front plate 800 and a rear plate 801. A plurality of pairs of linear transparent electrodes 803 are formed in a first substrate 802 which is a transparent substrate constituting the front plate 800. A plurality of pairs of linear electrodes 805 orthogonal to the linear transparent electrodes are disposed in parallel in a second substrate 804 constituting the rear plate 801. These two substrates are opposed to each other with a barrier rib 806 in which a phosphor layer is formed being interposed therebetween, and discharge gas is encapsulated in the barrier rib 806. When a voltage equal to or larger than a threshold is applied to between the electrodes of both the substrates, electricity is discharged at positions where the electrodes are orthogonal to each other and the discharge gas emits light, so that the emitted light can be observed through the transparent first substrate 802. Then, by controlling the electric discharge positions (electric discharge points), images may be displayed on the side of the first substrate. For achieving color display by the PDP, phosphors which develop desired colors by ultraviolet rays emitted at each electric discharge point during electric discharge are formed at positions (partition walls of the barrier rib) corresponding to respective electric discharge points For achieving full color display, phosphors of RGB (Red, Green, Blue) are formed.
More detailed description will be given of the structure of the front plate 800 and the rear plate 801.
In the front plate 800, a plurality of pairs of linear transparent electrodes 803, one pair being composed of two electrodes, are formed in parallel by ITO or other techniques on the inner face side of the first substrate 802 which is made of a transparent substrate such as glass substrates. A bus electrode 807 is formed on the inner face side-surface of the linear transparent electrodes 803 for decreasing a line resistance value. A dielectric layer 808 for covering these transparent electrodes 803 and the bus electrode 807 is structured to be formed over the entire inner face region of the front plate, and an MgO layer 809 that is a protective layer is structured to be formed on the entire surface region of the dielectric layer 808.
On the inner face side of the second substrate 804 of the rear plate 801, a plurality of linear address electrodes 805 orthogonal to the linear transparent electrodes 803 of the front plate 800 are formed in parallel from silver and other materials. Moreover, a dielectric layer 810 covering the address electrodes 805 is formed on the entire inner face region of the rear plate. On the dielectric layer 810, barrier ribs (partition wall) 806 of a specified height are formed in the state of protruding between the respective address electrodes for separating the respective address electrodes 805 and maintaining a gap interval between the front plate 800 and the rear plate 801 constant. With the barrier ribs 806, cells 811 are formed along the respective address electrodes, and phosphors 812 of each color of RGB are formed in sequence on its inner face. PDPs of cell structure include those having electric discharge points one in an independent cell as shown in FIG. 39 and those having a cell structure (unshown) partitioned by partition walls per line. In recent years, the “independent cell method” is drawing attention as a method allowing enhanced performance of PDP. This is because encircling the four sides of the cell by barrier ribs in a waffle-like state makes it possible to prevent light leakage between adjacent cells and to increase areas of emitters. As a result, it becomes possible to enhance luminous efficacy and luminous quantity (luminance), thereby making it possible to realize images of high contrast. These are considered as characteristics of the “independent cell method”. The phosphor layers formed on cell wall faces are generally formed to be as thick as about 10 to 40 μm for better color development. For forming the RGB phosphor layers, each cell is filled with a phosphor coating liquid and then is dried to remove volatile components, by which a thick phosphor is formed on the cell inner face and at the same time a space to be filled with discharge gas is created. For forming such a thick-film phosphors pattern, coating materials containing phosphors are prepared to be high-viscosity fluid pastes (phosphor pastes) of a few thousand mPa·s to tens of thousands mPa·s with a reduced quantity of solvent, and are conventionally discharged to substrates by screen printing or photo lithography.
(2) Issue in Conventional Screen Printing Method
Conventionally, in the case of employing the screen printing method, upsizing of screens caused extensive elongation of screen plates due to tension and this brought difficulty to high-accuracy alignment of the screen printing plate across the entire screen. Moreover, an attempt to fill phosphor materials caused the materials to be extensively put on top portions of the partition walls, which became an issue leading to cross talk between the barrier ribs in the case of the “independent cell method”. Eventually, it has became necessary to take actions such as introducing surface treatment or processing by mechanical means such as a polishing step for removing materials attached to the top portions of the partition walls. Further, a difference in squeegee pressure changes a fill of phosphor materials, and its pressure adjustment requires extreme delicacy and mostly depends on a level of skill of operators. Therefore, it is not easy to provide a constant fill to all the independent cells across the entire region of the rear plate.
(3) Issue in Conventional Photo Lithography
Conventionally, the photo lithography has a following issue. In this method, after a photosensitive phosphor paste is injected into the cells between the ribs, only photosensitive compositions injected into specified cells remain through exposing and developing steps. After that, through a burning step, organic substances in the photosensitive compositions are eliminated to form phosphor layer patterns. In this method, the paste for use contains phosphor powders and therefore its sensitivity to ultraviolet rays is low, which makes it difficult to form the phosphor layers to have a film thickness of 10 μm or larger. This has caused such an issue that sufficient luminance is unavailable.
Further, in the case of employing the photo lithography, the exposing and developing steps are essential for each color, and since phosphors are contained at high concentration in the coating layer of the paste, a loss of the phosphors due to removal through development is large and an effective utility of the phosphors is at best less than 30%, causing a serious issue costwise.
[2] Issue in the Case of Direct Patterning of Phosphor Layers With Use of the Conventional Dispenser Technique
Discharging a fluid to image tubes has conventionally been attempted with use of a dispenser of air nozzle type (FIG. 36) widely used in the filed such as circuit mounting. In the case of the air nozzle type, it is difficult to continuously discharge a high-viscosity fluid at high speed, and therefore fine particles are discharged in the state of being diluted by a low-viscosity fluid. In the case of discharging phosphors for image tubes such as PDPs and CRTs, diameters of fine particles are 3 to 9 μm and their specific gravities are about 4 to 5. In this case, there has been such an issue that a particle itself is heavy and therefore the moment the flow of a fluid stops, fine particles accumulate in flow passages. Further, dispensers of air method have a drawback of poor responsibility. This drawback is attributed to compressibility of air encapsulated by a cylinder and nozzle resistance generated when the air passes through a narrow space. More particularly, in the case of the air method, a time constant determined by the volume of the cylinder and the nozzle resistance is large, which makes it necessary to allow delay of about 0.07 to 0.1 sec. till a fluid is transferred onto a substrate after an input pulse is applied and discharge of the fluid is started.
Development has been made for applying the inkjet method widely used in commercial printers to industrial dispensing apparatuses. In the case of the inkjet method, the viscosity of a fluid is limited to 10 to 50 mPa·s due to constraints of its driving method and structure, and this makes it impossible to support a high-viscosity fluid.
In order to draw fine patterns by using the inkjet method, a low-viscosity nano-paste in which particles with an average diameter of about 5 nm are covered with dispersants and are independently dispersed has been developed. Assumed is a case in which phosphor layers are formed on inner walls of the barrier ribs (partition walls) of the above-described “independent cells” of the PDPs with use of the nano-paste. In the drying process after each cell is filled with a phosphor coating liquid, since the phosphor layers are basically given a thickness of about 10 to 40 μm as described before, a high-viscosity fluid paste with a reduced quantity of solvent is used as the coating material containing phosphors. In the low-viscosity nano-paste in which phosphor content can only be decreased, absolute content of the phosphors falls short, leading to failure in formation of the phosphor layers with a specified thickness. Further, while phosphor particles each with a diameter of several micron orders are generally considered optimum for the displays to have high intensity, it is not easy to change the phosphor diameter at the present stage, and this is one of the serious issues of the inkjet method.
The jet-type dispenser shown in FIG. 37 is sufficiently high in discharge speed compared to the conventional dispensers of air-type, thread groove-type, or other types and is also capable of supporting a high-viscosity fluid. Moreover, this method enables the fluid to fly from a nozzle for intermittent discharge in the state that the nozzle is sufficiently away from an opposed face. Thus, a discharging method involving the fluid flying from the nozzle is difficult to apply to the air-type or thread groove-type dispensers which cannot develop steep and pulsed pressure.
This method as described before is the method in which a spherically-shaped convex portion formed on the end portion of the needle 555 and a spherically-shaped concave portion formed on the discharge side are engaged to create an enclosed (hermetic) space 563 except the discharge nozzle 562, and the enclosed space is compressed to generate high pressure which allows a fluid to fly and flow away.
In this case, in the compressing step, a clearance between relatively moving members (convex portion and concave portion) in the suction portion 564 is zero, and phosphor particles with an average diameter of 3 to 9 μm are subjected to the action of mechanical compression and are destroyed. It's often the case that various failures caused as a result, such as clogging in flow passages and degradation of sealing performance of the suction portion 564 due to ware of the members make it difficult to apply this method to discharge of powder and granular materials such as phosphors.
Another issue in this method is difficulty in ensuring accuracy of an absolute discharge quantity per dot in the assumption of long time continuous use. In the assumption that phosphors are intermittently discharged into the above-described “independent cells” of the PDP, the necessary number of heads is several dozen in consideration of production process time in mass production. In the aforementioned dispenser, a discharge quantity per dot is determined by a volume of the enclosed space, i.e., a stroke of the needle 555 and sealing performance of the suction portion 564. However, it is expected to be extremely difficult from a practical standpoint to maintain the stroke and the absolute position of each needle 555 of several dozen of dispensers as well as the sealing performance of the suction portion 564 subject to wear in a constant state over a long period of time without dispersion.
In summary of these considerations, a method having a potential to substitute the screen printing method, e.g., a direct patterning method realizing formation of independent cell phosphor layers for PDPs, is not available at the present stage.
In order to satisfy various demands of recent years regarding fluid discharge in a very small flow quantity, the inventor of the present invention has proposed a discharge method for controlling a discharge quantity by applying relative linear motion and rotational motion to between a piston and a cylinder, providing a means to transport a fluid by the rotational motion, and changing a relative gap between a fixed side and a rotation side by using the linear motion, and a patent application thereof has been filed as “Fluid Feed Device and Fluid Feed Method) (Japanese Patent Application No. 2000-188899 (U.S. Pat. No. 6,558,127 and U.S. Pat. No. 6,679,685)).
Further, after theoretical analysis was applied to the dispenser structure disclosed in the proposal, the inventor has already proposed a method and a device for intermittent discharge (Japanese Patent Application No. 2001-110945 (U.S. Pat. No. 6,679,685)) to utilize squeeze effect produced by steep change of a clearance between an end face of the piston and its relative movement face.
As a result of performing strict theoretical analysis, the inventor of the present invention has found out that by adjusting the combination of pump characteristics and pistons, a developed pressure (secondary squeeze pressure) equal to or larger than the squeeze effect can be obtained even in the case where a clearance between the end face of the piston and the relative movement face is sufficiently wide. Since this effect allows simple management of the clearance between the end faces of the piston and makes it possible to set a total discharge quantity per dot by a number of revolutions of the pump, it becomes possible to realize a very-high-speed intermittent discharge device which is easily handled in a practical use, has high flow quantity accuracy, and has high reliability with respect to powder and granular materials, and the device has already proposed (Japanese Patent Application No. 2002-286741 (U.S. patent application Ser. No. 10/673,495)).
In Japanese Patent Application No. 2003-036434 (U.S. patent application Ser. No. 10/776,278) following the above proposal, the inventor of the present invention has found out that compressibility possessed by fluid exerts a large influence on development of squeeze pressure, and has proposed a head structure which realizes high-speed intermittent discharge and high-speed continuous discharge based on the knowledge obtained from the analysis result concluded in consideration of the compressibility.
As a result of advanced research with strict comparison between the theoretical analysis and experimental results on the basis of these proposals, it is an object of the present invention to provide fluid injection method and apparatus and a display panel, which are capable of offering high responsibility even in the case where a volume of flow passages increases due to adoption of multi-head structure or the like.